\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usepackage{wasysym}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\begin{document}
\small
\begin{tikzpicture}[>=latex,scale=1]
  \fill[pattern =north east lines] (-2,0)rectangle(2,-0.25);
  \draw[thick] (-2,0)--(2,0);
  \draw[thin,densely dashdotted](0,0)--(0,2.5)node [above]{法线};
  \draw[semithick,postaction={decorate},decoration={markings,mark=between positions 0.25 and 0.75 step 0.5 with {\arrow{>}}}] (135:2)node [above]{入射光线}--(0,0)--(45:2)node [above]{反射光线};  
  \draw (0,.65) arc (90:45:.65) node [midway,above]{$r$};	
  \draw (0,.5) arc (90:135:.5)node [midway,above]{$i$};
\end{tikzpicture}
\end{document}